When writing a multithreaded application, you should evaluate all the parts of the application and all the services that it uses for thread safety.
How each service or API that is used by the application uses its storage resources is an important consideration for providing threadsafe applications. If you do not use storage in a threadsafe manner, data in your application is likely to be damaged.
Other critical aspects in creating threadsafe applications are the APIs and system services on which your application or your application services rely. To be threadsafe, your storage usage and all APIs and services that you use directly or indirectly must be threadsafe. APIs and system resources that you use indirectly are particularly difficult to evaluate. See the APIs topic for the specific APIs or system services you use to see if they are thread safe.
You will probably call system services, APIs, or other applications for which you do not have the source code. Many of these services are not be classified as threadsafe or non-threadsafe. You must assume that the services are not threadsafe.